(a) Field of the Invention
The present invention relates to a thin film transistor array panel and a manufacturing method thereof, and in particular, to a thin film transistor array panel for an organic electro-luminescence display device.
(b) Description of the Related Art
Generally, an organic electro-luminescence (EL) display is a self emissive display device, which displays images by exciting an emissive organic material to emit light. The organic EL display includes an anode (hole injection electrode), a cathode (electron injection electrode), and an organic light emission layer interposed therebetween. When the holes and the electrons are injected into the light emission layer, they are recombined and pair annihilated with emitting light. The light emission layer further includes an electron transport layer (ETL) and a hole transport layer (HTL) as well as an electron injecting layer (EIL) and a hole injecting layer (HIL) for enhancing the light emission.
A plurality of pixels of the organic EL display, each including an anode, a cathode, and a light emission layer, are arranged in a matrix and driven in passive matrix (or simple matrix) addressing or active matrix addressing.
The passive matrix type organic EL display includes a plurality of anode lines, a plurality of cathode lines intersecting the anode lines, and a plurality of pixels, each including a light emission layer. The selection of one of the anode lines and one of the cathode lines cause light emission of a pixel located at the intersection of the selected signal lines.
The active matrix type organic EL display includes a plurality of pixels, each including a switching transistor and a driving transistor as well as an anode, a cathode, and a light emission layer. The EL display further includes a plurality of gate lines transmitting gate signals and a plurality of data lines transmitting data voltages. The switching transistor is connected to one of the gate lines and one of the data lines and transmits the data voltage from the data line in response to the gate signal. The driving transistor receives the data voltage from the switching transistor and drives a current depending on the data voltage. The current from the driving transistor enters the light emission layer to cause light emission having an intensity depending on the current. The color representation of the EL display is obtained by providing red, green and blue light emission layers.
The EL display significantly requires uniformity in characteristics of the driving transistors since the difference in the characteristics of the driving transistors results in the difference in the luminance of a display screen for the same gray.
The transistors may be polysilicon thin film transistors (TFTs) and the characteristics of the polysilicon TFTs significantly depend on a crystallization process. When using an eximer laser annealing (ELA), the illuminated areas are linear and non-uniform energy of the illumination steps may results in the linear areas with different device characteristics, which can be easily conceived. A sequential lateral solidification (SLS) improves the uniformity in the device characteristics of the TFTs, but it is not sufficient since the laser beam has inevitable energy deviation of about ±10%.